Optionally clear PlatformCanvas instances.

skia/ext/bitmap_platform_device_mac.cc

Index: skia/ext/bitmap_platform_device_mac.cc
===================================================================
--- skia/ext/bitmap_platform_device_mac.cc	(revision 127021)
+++ skia/ext/bitmap_platform_device_mac.cc	(working copy)
@@ -125,11 +125,6 @@
     bitmap.setPixels(data);
   } else {
     data = bitmap.getPixels();
-
-    // Note: The Windows implementation clears the Bitmap later on.
-    // This bears mentioning since removal of this line makes the
-    // unit tests only fail periodically (or when MallocPreScribble is set).
-    bitmap.eraseARGB(0, 0, 0, 0);
   }
 
   bitmap.setIsOpaque(is_opaque);
@@ -160,6 +155,15 @@
   return rv;
 }
 
+BitmapPlatformDevice* BitmapPlatformDevice::CreateAndClear(int width,
+                                                           int height,
+                                                           bool is_opaque) {
+  BitmapPlatformDevice* device = Create(NULL, width, height, is_opaque);
+  if (!is_opaque)
+    device->accessBitmap(true).eraseARGB(0, 0, 0, 0);
+  return device;
+}
+
 BitmapPlatformDevice* BitmapPlatformDevice::CreateWithData(uint8_t* data,
                                                            int width,
                                                            int height,
@@ -242,7 +246,9 @@
     SkBitmap::Config config, int width, int height, bool isOpaque,
     Usage /*usage*/) {
   SkASSERT(config == SkBitmap::kARGB_8888_Config);
-  return BitmapPlatformDevice::Create(NULL, width, height, isOpaque);
+  SkDevice* bitmap_device = BitmapPlatformDevice::CreateAndClear(width, height,
+                                                                 isOpaque);
+  return bitmap_device;
 }
 
 }  // namespace skia